Process and agents to remove metals from high-boiling hydrocarbon fractions

ABSTRACT

The object of the invention is a process and agents to remove metal contaminants from hydrocarbon fractions like those obtained as a product from the Fischer-Tropsch synthesis involving the use of suspended catalyst. As per the present invention, the feed hydrocarbon fraction is treated with a demetallizing agent, comprising at least one sulfur source and at least one basic compound, under anhydrous conditions. The metals to be removed are obtained in the form of precipitate that can be easily separated by means of a mechanical separation process such as filtration, for example.

FIELD OF THE INVENTION

This invention relates to a process for the removal of metals from high-boiling hydrocarbon fractions as well as agents to their removal. In particular, the invention relates to a process and agents to separate nickel, cobalt and aluminum contaminants originating from catalysts and contained in the primary products of a hydrocarbon synthesis, e.g. pursuant to the Fischer-Tropsch process.

DESCRIPTION OF THE PRIOR ART

Hydrocarbons can be generated as synthesis products from chemical-catalytic processes like for example the Fischer-Tropsch process, the basics of which have been described in great detail in specialist literature, e.g. in Ullmann's Encyclopedia of Industrial Chemistry, sixth Edition, 1998 Electronic Release, key word “Coal Liquefaction”, chapter 2.2 “Fischer-Tropsch Synthesis”. A modern process variant is the conversion of synthesis gas in a suspension of solid, fine-grain catalyst in the liquid product hydrocarbons (so-called slurry process). In this process, high-activity catalysts are used whose active components contain metals such as cobalt and a support material such as alumina, as described in U.S. Pat. No. 4,801,573. The international patent application WO 98/27181 A1—in addition to numerous other publications—proposes a process for the separation of catalyst suspension from the hydrocarbon product. The product hydrocarbons obtained in the process frequently contain significant amounts of heavy metals. The possible reasons for such undesired heavy metal contamination are abrasion and corrosion processes occurring on the catalysts and/or tank material used in the synthesis process. However, these methods based on mechanical separation processes are only suited for the separation of particulate metal contaminants and not for the separation of chemically bonded or finely dispersed and/or colloidal metals in the hydrocarbon phase.

In addition to the heavy metal contamination also contamination with the metal of the catalyst support matrix (e.g. aluminum) is observed. The metal contamination described may be disruptive for a further chemical-catalytic conversion of the product hydrocarbons since it may act as catalyst poison. Moreover, heavy metal contamination, irrespective in which substance it is contained, represents a potential environmental and health hazard. In particular, nickel and cobalt have to be mentioned here which are classified as carcinogenic. On the other hand, both heavy metals represent valuable catalyst elements that should be recycled in order to prevent losses.

The prior art already knows various processes for the separation of metal contaminants from hydrocarbons. The publications AT 205229, DD 26308, EP 0009935 B1, GB 1001190, U.S. Pat. No. 3,449,243, U.S. Pat. No. 3,617,530 and WO 2009113095 A2 describe washing processes for the removal of metal contaminants from hydrocarbon phases. In these processes, the hydrocarbon phases are either treated with aqueous solutions of certain reagents or by addition of reagents to the organic phase with subsequent water wash to dissolve the metal contaminants and transfer them into the aqueous phase. The downsides of these processes are the work required for the treatment and subsequent separation of the two-phase mixture of hydrocarbon phase and aqueous phase as well as the treatment of the aqueous phase required prior to its disposal or re-use.

The German patent publication DE 1212662 describes a process for the treatment of hydrocarbon oils for the purpose of removing metallic contaminants that are detrimental for the catalysts used for their conversion. Here, it is proposed to treat the contaminated hydrocarbon oils with a solution of hydrogen fluoride in an organic solvent whereby the metals are converted into a hardly soluble precipitate that can be separated in a downstream step by means of a mechanical separation process. This way, the above-described problems during the treatment of a two-phase mixture of hydrocarbon phase and aqueous phase are avoided. However, the use of a highly reactive, gaseous hydrogen fluoride for the preparation of the treatment solution represents a downside for reasons of occupational safety and handling.

The DE patent application 2346058 shows a process for the removal of metal-containing impurities from a hydrocarbon material by contacting this material with a catalyst under hydrogenation conditions whereby the metal-containing contaminants are reduced to an elementary metal that is separated from the hydrocarbon phase as a precipitate. The downside of this process is the complex process control to ensure a largely complete hydrogenation of the metallic contaminants while at the same time avoiding the hydrogenating cracking of the hydrocarbons.

The U.S. Pat. No. 4,518,484 describes a process for the treatment of metal-containing hydrocarbon feed streams that involves the following steps: (a) contacting the hydrocarbon feed streams in an extraction zone with at least one hydrocarbon solvent containing from 2 to 10 carbon atoms per molecule under supercritical conditions in the presence of a demetallizing agent based on an organophosphorus chemical, (b) recovering an overhead stream from the extraction zone that contains hydrocarbons substantially reduced in contaminating metals content and a bottoms product that contains the metal-laden solvent. One downside is the complex process control, especially the creation of supercritical conditions.

DESCRIPTION OF THE INVENTION

The underlying task of the present invention therefore is to present a simple technology for the removal of metal contaminants from high-boiling hydrocarbon fractions and adequate means for performing such removal characterized by a simple process—in particular one without the use of aqueous media—that can be applied without the use of substances involving a high risk potential.

The solution as per this invention mainly results from the features of the characterising portion claim 1 in conjunction with the features of the precharacterising portion of the claim in that—in a process to obtain a hydrocarbon fraction with a low metals content, whereby the metals in the hydrocarbon fraction are chemically bonded or dispersed in colloidal or finely dispersed form in the hydrocarbon fraction, a demetallizing agent is added to the liquid hydrocarbon fraction that comprises the following components:

-   -   (a) at least one sulfur source that is at least partially         soluble in the hydrocarbon fraction,     -   (b) at least one basic compound that is at least partially         soluble in the hydrocarbon fraction,         and that, after addition of the demetallizing agent, the metals         are precipitated in the form of a hardly soluble precipitate and         separated by means of a mechanical separation process.

Other advantageous embodiments of the invention result from the sub-claims. The invention also relates to a demetallizing agent as per claims 2 through 6.

For the treatment according to the process that is the object of this invention, the feed hydrocarbon fraction to be treated must be liquid. Wax-like hydrocarbons, like for example those obtained as a product of the Fischer-Tropsch process, must be molten prior to the treatment, where necessary.

It is known that metals such as nickel or cobalt in the form of their insoluble sulfides precipitate from aqueous solutions and can thus be quantitatively separated from inorganic multi-metal mixtures. This requires sulfide ions (S²⁻) and defined basic conditions or, to be more exact, a pH of ≧8 (Jander; Blasius, “Lehrbuch der analytischen and praparativen anorganischen Chemie”, 14^(th) edition, Hirzel Verlag, Stuttgart 1995). Surprisingly, it showed that this principle of the separation of nickel and cobalt from metalcontaminated hydrocarbons by precipitation as sulfides could be transferred to the prevailing anhydrous conditions. Here, comparative tests have shown that the presence of a basic compound is essential for the reaction. This permits to conclude that the reaction most probably takes place via intermediate sulfides and/or hydrogen sulfide that forms. Also a direct, base-catalyzed reaction of the sulfur source with the free or bonded metals would be conceivable.

Especially advantageous is the fact that, with the removal of nickel and cobalt, also a complete removal of aluminum contaminants originating from the support material was achieved. Hence, a possibility was discovered to achieve a depletion of nickel and cobalt together with other metals such as aluminum in a simple, single-step process. The resulting metal sulfides precipitate from the reaction mixture as a compact precipitate that can very easily be separated by an adequate mechanical separation process and that, in this highly concentrated form, can be routed to metal recycling.

The reaction to form metal sulfides from divalent metals (Ni, Co) can be described as follows:

$\begin{matrix} {Me}^{2 +} & + & S^{2 -} & = & {MeS} \\ {{Metal}\mspace{14mu} {ion}} & \; & {{Sulfide}\mspace{14mu} {ion}} & = & {{Metal}\mspace{14mu} ({II})\mspace{14mu} {sulfide}} \end{matrix}$

In order to obtain the sulfide concentration needed for the precipitation as per this invention, two requirements have to be met:

-   -   (a) The existence of a base that is at least partially soluble         in the hydrocarbon. Examples could be ammonia, amines, alkanol         amines, pyridines, ammonium, phosphonium and sulfonium         compounds; in principle, also other basic compounds are possible         that are at least partially soluble in the hydrocarbon phase to         be treated.     -   (b) The existence of a sulfur source. Examples for a sulfur         source are: organic sulfur compounds such as thiourea,         thiocarbonates, dithiocarbonates, thiocarbamates,         dithiocarbamates, mercaptanes, organic disulfides, organic         polysulfides, thioacid amides; inorganic sulfur compounds such         as gaseous hydrogen sulfide, ammonium sulfide, inorganic         monosulfides, inorganic disulfides, inorganic polysulfides or         elementary sulfur. In principle, any sulfur-containing compound         can be used in the present invention that is in a position to         produce or provide sulfide ions and/or active sulfur atoms for         the precipitation reaction under the process conditions.

OTHER PREFERRED EMBODIMENTS OF THE INVENTION

In a preferred embodiment of the invention elementary sulfur is used as a sulfur source. It can be added to the hydrocarbon fraction to be treated as a powder while stirring, whereby it dissolves homogenously in the hydrocarbon.

In another preferred embodiment, the process as per the present invention is conducted using a demetallizing agent comprising sulfur-impregnated activated carbon as its sulfur source. Here, it is advantageous that, at the treating temperatures required, the formation of molten sulfur is avoided which could solidify in colder areas of the treatment facility and lead to incrustations or obstructions in such areas. The sulfur-impregnated activated carbon that is added as a powder or as a shaped body, e.g. in the form of extrudates, retains its texture and characteristics and can be separated easily by means of a mechanical separation process.

In another embodiment of the process as per the present invention it is planned that gaseous hydrogen sulfide as a sulfur source is added to the hydrocarbon fraction.

The separation of the metal-containing, hardly soluble precipitate as per the present invention is done by means of a mechanical separation process, preferably by filtration, sedimentation, decantation or centrifugation, or combinations thereof.

In another embodiment of the process as per this invention sulfur-impregnated activated carbon is used as a demetallizing agent and, after addition of a base, the hydrocarbon fraction to be treated is fed to a fixed bed reactor containing a bed of this demetallizing agent, whereby a metal-depleted hydrocarbon fraction is withdrawn as a product from the fixed bed reactor. This way, the effort required for separating the metal-containing, hardly soluble precipitate is reduced to a minimum.

By adding the sulfur-containing demetallizing agent, the sulfur content of the hydrocarbon fraction obtained as a product is increased significantly as compared to that of the feed hydrocarbon fraction. This might be advantageous depending on the type of intended use or for the processing of the product hydrocarbon fraction. The hydrocarbon synthesis according to the Fischer-Tropsch process where long-chain, wax-like hydrocarbon products are selectively generated, is often followed by a hydrocracking step that serves to generate short-chain hydrocarbons, like for example a diesel fraction or an Otto fuel fraction. For hydrocracking, frequently catalysts on a cobalt-molybdenum basis are used that reach their end activity through a prior sulfur treatment. Therefore, the further embodiment of the process as per the present invention provides for the use of the demetallized hydrocarbon fraction obtained in the process as per the present invention as a sulfur donor for the activation of sulfur-activated catalysts on the grounds of their higher sulfur content.

A higher sulfur content in the hydrocarbon fraction treated as per the present invention is not always acceptable. Another advantageous embodiment of the invention therefore provides for the use of organic sulfur compounds, preferably mercaptanes, and more specifically trimercapto-s-triazine, as the sulfur-containing demetallizing agent. Surprisingly, use of this component only results in a low increase of the sulfur content in the hydrocarbon fraction treated as per the present invention compared to the use of demetallizing agents on the basis of elementary sulfur.

EMBODIMENT AND NUMERICAL EXAMPLES

Further embodiments, advantages and application options of the invention also result from the non-exhaustive description below of embodiments and numerical examples. All characteristics, either alone or in any combination, form the invention, irrespective of their being summarized in the claims or related claims.

Example 1

1 kg of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis with a total metal content of around 325 ppm (nickel 100 ppm, cobalt 25 ppm, aluminum 200 ppm; determined by means of x-ray fluorescence analysis (XRF), evaluation by means of Uniquant 2 method)) were molten at 100° C. 200 mg of elementary sulfur powder as well as 1.2 g of triethanol amine were added to the melt. Both substances are homogeneously distributed in the liquid HC phase owing to vigorous stirring while heating up to 180° C. Then, the mixture was heated to 180° C. while vigorously stirring and this temperature perature was maintained for 5 minutes. Already starting from a temperature of 160° C., a distinct black-brown coloration could be observed which is caused by the NiS and/or CoS that forms. After stopping the stirring process a black-brown precipitate very quickly settled at the bottom of the reaction vessel. This precipitate was very easy to separate from the reaction mixture with the help of a folded filter. The analysis of the filtrate showed no detectable concentration of nickel, cobalt and aluminum (detection limit 5 ppm). The sulfur content in the filtrate amounted to around 150 ppm.

Example 2

1 kg of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis), with a total metal content of around 325 ppm (nickel 100 ppm, cobalt 25 ppm, aluminum 200 ppm) was molten at 100° C. The metal concentrations were determined as described under Example 1. 300 mg of elementary sulfur as well as 3 g of triethanol amine were added to the melt and homogeneously distributed in the liquid HC phase owing to vigorous stirring while heating up to 180° C. After that, the mixture was heated to 180 ° C. while vigorously stirring and this temperature was maintained for 5 minutes. Again, a distinct increase in black-brown coloration could be observed starting from a temperature of 160° C. which is caused by the NiS and/or CoS that forms. On stopping the stirring, a black-brown precipitate very quickly settled at the bottom of the reaction vessel. This precipitate was very easy to remove from the reaction mixture with the help of a folded filter. The analysis of the filtrate did not show any detectable concentration of nickel, cobalt and aluminum (detection limit 5 ppm). The sulfur content in the filtrate amounted to around 250 ppm, i.e. it was significantly higher than that in Example 1. This suggests that there is a possibility to control the sulfur content of the hydrocarbon product by the corresponding addition of the sulfur source above the stoichiometric quantity required for complete metal separation in order to optimally adjust it to downstream process steps, e.g. the sulfur activation of a Co—Mo hydrocracking catalyst. On the other hand and where required, the sulfur content in the hydrocarbon product can be reduced to a minimum by way of the corresponding metering.

Example 3

1 kg of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis) with a total metal content of around 325 ppm (nickel 100 ppm, cobalt 25 ppm, aluminum 200 ppm) was molten at 100° C. 10 g of Desorex HGD2S (activated carbon product by DONAU CARBON containing approx. 10-15% elementary sulfur in the form of 1/8″ extrudates), corresponding to a sulfur concentration of 1000-1500 ppm, as well as 0.5 g of triethanol amine were added to the melt. After that, the mixture was heated to a temperature of 185° C. within 30 minutes while vigorously stirring and this temperature was maintained for 5 minutes. Already starting from a temperature of 160° C. it was possible to observe a distinct black-brown coloration caused by the NiS and/or CoS that formed. Upon reaching a temperature of 185° C., formation of a precipitate in the form of flocculation was observed. On stopping the stirring, the hot reaction mixture was poured onto a folded filter. The precipitate could very easily be separated from the reaction mixture by filtration. The sulfur-impregnated activated carbon added to the mixture as extrudates remained intact with regard to its characteristics and texture and settled at the bottom of the reaction vessel after stopping the stirring. The analysis of the filtrate showed no detectable concentrations of nickel, cobalt and aluminum (detection limit 5 ppm). The sulfur content in the filtrate amounted to approx. 1,100 ppm.

Example 4

1 kg of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis) with a total metal content of approx. 325 ppm (nickel 100 ppm, cobalt 25 ppm, aluminum 200 ppm) was molten at 90° C. 200 mg of TAICROSS® TMT (Evonik Degussa GmbH) containing 98% trimercapto-S-triazine) were added to the melt. During stirring, the powder preparation initially did not dissolve in the molten wax and was merely suspended in this mixture. The solid substance only dissolved after adding 2 g of triethanol amine to the reaction mixture. This led to a distinct clouding of the liquid phase. After that, the mixture was stirred for another 10 minutes at 90-100° C. The clouding could then be very easily separated from the reaction mixture using a folded filter. The analysis of the filtrate did not produce a detectable concentration of nickel and aluminum (detection limit in each case: 5 ppm). The cobalt concentration amounted to 5 ppm, the sulfur content in the filtrate amounted to approx. 50 ppm. Leaving the filtrate in a drying cabinet for one hour resulted in slight clouding. A repeated filtering of this sample showed that no more cobalt can be detected in the filtrate. The sulfur content remained unchanged. In this context, the analyses of the metal and sulfur contents were again performed by means of x-ray fluorescence analysis (XRF) using the UNIQUANT 2 method.

Comparative Test

The test from Example 1 was repeated under the same conditions and with the same feed hydrocarbon mixture but without the addition of triethanol amine or another base. Even when heating to 180° C. no color change of the hydrocarbon phase and no precipitation could be observed. The subsequent XRF analysis of the hydrocarbon showed an unchanged metal content for the three individual metals and also for their sum within the analytical accuracy. Consequently, a base contained in the demetallizing agent is a condition precedent for the practicability of the process as per the present invention.

COMMERCIAL APPLICABILITY

With this invention, a process for the removal of metal contaminants from hydrocarbon fractions is provided which, compared to processes known from the prior art, is characterized by its simple equipment and by the absence of additional extraction agents, especially agents that do not relate to the process, such as aqueous solutions. Furthermore, it is advantageous that only substances with a low to medium hazard potential are used and that the use of substances with a high hazard potential such as hydrogen fluoride, is avoided. 

1-10. (canceled)
 11. A process for the production of a hydrocarbon fraction with low metal content, wherein metals contained in the hydrocarbon fraction are chemically bonded or dispersed in the hydrocarbon fraction in a colloidal or finely-dispersed form, wherein a demetallizing agent is added to the liquid hydrocarbon fraction comprising: (a) at least one sulfur source that is at least partially soluble in the hydrocarbon fraction, (b) at least one basic compound that is at least partially soluble in the hydrocarbon fraction, wherein after addition of the demetallizing agent, the metals are precipitated in the form of a precipitate and separated by means of a mechanical separation process.
 12. A demetallizing agent for hydrocarbon fractions, in particular for use in a process according to claim 11, comprising (a) at least one sulfur source that is at least partially soluble in hydrocarbon fractions, (b) at least one basic compound that is at least partially soluble in hydrocarbon fractions.
 13. The demetallizing agent according to claim 12, wherein at least one of the compounds below is selected as a sulfur source: thiourea, thiocarbonates, dithiocarbonates, thiocarbamates, dithiocarbamates, mercaptanes, organic disulfides, organic polysulfides, thioacid amides; hydrogen sulfide, ammonium sulfide, inorganic monosulfides, inorganic disulfides, inorganic polysulfides or elementary sulfur.
 14. The demetallizing agent according to claim 12, wherein at least one of the compounds below is selected as a basic compound: ammonia, amines, alkanol amines, preferably triethanol amine; pyridines, ammonium compounds, phosphonium compounds, sulfonium compounds.
 15. The demetallizing agent according to claim 13, wherein elementary sulfur or hydrogen sulfide is used as a sulfur source.
 16. The demetallizing agent according to claim 13, wherein sulfur-impregnated activated carbon is used as a sulfur source.
 17. The process according to claim 11, wherein filtration, sedimentation, decantation or centrifugation or combinations thereof are used as mechanical separation processes.
 18. The process according to claim 11, wherein sulfur-impregnated activated carbon is used as a sulfur source and that, after addition of the base, the hydrocarbon fraction to be treated is added to a bed of demetallizing agent in a fixed bed reactor whereby a metal-depleted hydrocarbon fraction is withdrawn as a product from the fixed bed reactor.
 19. The demetallizing agent according to claim 12, wherein mercaptanes, preferably trimercapto-s-triazine, are used as a sulfur source. 